A fiber optic cable may typically contain a plurality of bundles of optical fibers, each bundle having from dozens to hundreds of optical fibers. Each optical fiber typically has a fiber optic core consisting of a glass tube with refractive properties selected to contain electromagnetic transmissions. Radiating concentrically from the core may be a plurality of layers, often of alternating dielectric and conductive materials, housed in a protective jacket, which forms the exterior concentric layer of the fiber. For example, one layer might consist of a hygroscopic material to exclude water from the cable to keep the cable dry, while another layer might consist of an insulator to protect the cable from electrical surges or lightning hits.
Additionally, one or more protective sheaths are often among the layers interior to the jacket. Typically, the purpose of the sheaths is to stiffen the cable so that the cable cannot bend so far as to damage the glass fiber optical core. The sheaths are frequently composed of copper fiber that is suitably disposed around an interior layer. It is not uncommon that one or more sheaths are composed of braided copper wire formed into a tube, when viewed in isolation from the cable.